This invention relates to diaphragm gas meters and, more particularly, to an improved adjustable tangent assembly for use therewith.
Positive displacement diaphragm gas meters typically are provided with a tangent which drivingly couples the diaphragm driven flag assembly to the crank shaft which is in turn coupled to open and close the slide valves of the meter. It is common practice to provide an adjustable tangent so that the timing of the valves and the stroke of the diaphragms may be adjusted to calibrate the meter. Existing arrangements for providing such an adjustable tangent suffer from a number of drawbacks. A very serious drawback is the requirement for a large "handhole" in the meter cover to afford access to the tangent adjustment screws within the gas distribution chamber area. This large handhole necessitates the provision of a gasket and screws to secure the handhole cover. Often, tie wires and seals are required to provide tamper resistance.
Other deficiencies of existing designs include difficulty of adjustment due to space restrictions and further that whatever adjustment is made, the resolution of such adjustment is relatively crude. Additionally, adjustment with external tools is very difficult due to the internal location and the configuration of the adjustment screws. Accordingly, automated adjustment is not possible. Still further, in most designs, the stroke adjustment affects the timing, and the timing adjustment affects the stroke.
It is therefore an object of this invention to provide an improved adjustable tangent assembly.
It is another object of this invention to provide such an assembly which is adjustable from outside the meter.
It is a further object of this invention to provide such an assembly which is amenable to automated adjustment.
It is still another object of this invention to provide a tool for use with the adjustable tangent assembly.
It is yet another object of this invention to provide an adjustable tangent assembly wherein the timing and stroke adjustments are independent from each other.
It is another object of this invention to provide an adjustable tangent assembly wherein only a minimal opening in the meter cover is required.
It is another object of this invention to provide an adjustable tangent assembly having a high adjustment resolution.
It is another object of this invention to provide an adjustable tangent assembly wherein the adjustment mechanism is self-locking.